In the production of printed circuit boards, solid circuits are formed of a conductive material positioned on opposite sides of a boardlike insulating base and one or more metal foil sheets are imbedded internally in the base and function as signal, power or ground planes. In order that electrical connections may be established from the circuit made by the conductor on one side of the board to the conductor on the other side of the nonconducting board as well as to the internal planes, it is common practice to form holes through the board and to conductively connect the circuit conductors and planes through these holes. These holes are called "through holes" or via holes and the connections may be by mechanical means such as rivets, eyelets or pins or by coating means such as electroplating a metallic conductor on the surface of the via hole and subsequently soldering an input/output pin in the plated hole.
A significant problem in high density multilayer printed circuit boards is how to accommodate the need for an engineering change capability. In the early version of the printed circuit board, the connection between a plated via hole and an internal signal, power or ground plane was buried in the board and it was impossible to delete the plane from the circuit to make an engineering change without ruining the board. To overcome this problem, a later board configuration was developed wherein each plated via hole was connected to the signal, power or ground plane by way of an associated redundant plated via hole with the holes being interconnected by a metallic strip on the surface of the board. An engineering change could be made by simply cutting the connector strip on the board surface and changing the wiring. Although this provided improved change capability, the use of redundant vias consumes a substantial amount of total board real estate available for making circuit lines and interconnections thereby severely limiting the overall capability of the board and also conceivably affecting the reliability of the resultant structure. It became evident that an improved via arrangement was needed which would give the desired change capability without using an excess of board real estate.